TOKYO--Hitachi Vehicle Energy will supply lithium ion batteries for the Buick LaCrosse this summer, the Japanese company's first lithium power pack for a passenger vehicle.

Yoshito Tsunoda, senior vice president for battery systems at Hitachi, said the deal is part of Hitachi's plan to enter the growing battery market for hybrid and electric vehicles. The LaCrosse uses mild hybrid technology, called eAssist.

The compact 115-volt, 0.5 kilowatt-hour lithium ion battery was displayed publicly for the first time at the International Rechargeable Battery Expo that opened last week in Tokyo.

Hitachi's battery will power the eAssist system that General Motors says will help the 2012 LaCrosse get 25 percent better fuel economy than the 2011 LaCrosse. The eAssist system uses stop-start technology and an electric motor boost to help the car accelerate.

The battery is not strong enough to drive the LaCrosse in electric-only mode, said Kosuke Inoue, group leader of production engineering at Hitachi. Production of the battery, which uses 32 cylindrical cells, began in January at a plant in Ibaraki prefecture, north of Tokyo.

The LaCrosse gets Hitachi's third-generation lithium ion batteries. Fourth-generation batteries, which will deliver about 1.5 times the energy output, likely will go into production in 2013, Inoue said.

So far most of Hitachi's lithium ion batteries have gone into trucks and buses. Inoue said the LaCrosse will be the first passenger vehicle to get them.